The present invention relates to a fullerene derivative which has DNA compacting activity and is useful as a DNA compaction reagent, among other uses, and is applicable, for example, in the pharmaceutical industry.
DNA compaction in a protein-DNA complex such as the arrangement of DNAs on a chromosome is a very important subject of biochemical research. Compaction by organic micromolecules and inorganic ions is also an important subject of research relevant to transfection [e.g. Yoshikawa, Y. et al., FEBS Letters, 1996, vol. 396, 71-76; Behr, J-P, Acc. Chem. Res., 1993, vol. 26, 274-278; etc.].
The present invention has for its object to provide a novel means for DNA compaction.
Thus far has been provided a technology for use-tailored modification of fullerene, and a variety of fullerene derivatives have been synthesized [e.g. Friedman, S. H. et al. J. Am. Chem. Soc., 1993, vol. 115, 6506-6509; Yamago, S. et al., J. Am. Chem. Soc., 1994, vol. 116, 1123; Taki, M. et al., J. Am. Chem. Soc., 1997, vol. 119, 926; An, Y. Z. et al., Tetrahedron, 1996, vol. 52, 5179-5189; Nakamura, E. et al., Bull. Chem. Soc. Jpn., 1996, vol. 69, 2143-2151; Yamago, S. et al., Chemistry Letters, 1996, 395-396; Murata, Y. et al., The 2nd International Forum on Chemistry of Functional Organic Chemicals (IFOC-2), 1997, P-31, Tokyo, Japan, etc.].
The inventors of the present invention discovered that, among such fullerene derivatives, fullerene derivatives having 1 to 4, nitrogen-containing hydrophilic side chain(s), inclusive of salts thereof, are amphiphilic and have exceptionally high DNA-compacting activity and have accordingly developed the present invention.
The fullerene derivative of the present invention is a xe2x80x9cfullerene derivative having 1 to 4, nitrogen-containing hydrophilic side chain(s)xe2x80x9d. This fullerene derivative includes not only novel compounds but also known compounds.
The DNA-compacting activity of the fullerene derivative of the present invention is the result of an interplay of the size and hydrophobicity of fullerene and the affinity of the nitrogen-containing hydrophilic side chain(s) of the derivative for the phosphate group. It is supposed that the interaction between fullerene and the hydrophobic moieties of a DNA (e.g. major grooves of the DNA) and the interaction between the nitrogen-containing hydrophilic side chain(s) and the phosphate group of the DNA causes the DNA unimolecule to be bent and folded, and that the hydrophobic moieties of a large number of such folded DNA unimolecules coalesce to cause said compaction.
Therefore, the molecular design of a fullerene derivative may be made liberally by one skilled in the art with the above mechanism taken into consideration. The DNA-compacting activity of the fullerene derivative synthesized accordingly can be evaluated by electrophoresis of a mixed solution of the fullerene derivative and a DNA (e.g. plasmid DNA) and measuring the amount of DNA. Moreover, since this compacting activity of the fullerene derivative is closely associated with the high binding affinity of the derivative for DNA, a screening can be made by an ethidium bromide displacement assay using calf thymus DNA.
While the fullerene derivative may be used in the form of a salt, the salt is preferably a conventionally nontoxic salt, particularly a pharmaceutically acceptable salt. More particularly, the salt includes inorganic acid salts (e.g. hydrochloride, hydrobromide, sulfate, phosphate, etc.), organic carboxylic acid or sulfonic acid salts (e.g. formate, acetate, trifluoroacetate, maleate, tartrate, fumarate, methanesulfonate, benzenesulfonate, toluenesulfonate, etc.), and salts with basic or acidic amino acids (e.g. arginine, aspartic acid, glutamic acid, etc.).
The fullerene derivative may occur as various isomers owing to the presence of asymmetric carbon and molecular asymmetry and any and all of them are subsumed under the concept of fullerene derivative according to the present invention.
The xe2x80x9cfullerenexe2x80x9d of the fullerene derivative of the present invention is not restricted to [60]fullerene but includes higher-order fullerenes (e.g. [70]fullerene etc.).
The preferred xe2x80x9cnitrogen-containing hydrophilic side chainxe2x80x9d includes xe2x80x9ca hydrocarbon group which has 1 or 2 straight-chain or branched-chain substituent group(s) each comprising 1 to 10 nitrogen atom(s) and 2 to 30 carbon atoms, and is configured to be bonded to 1 or 2 of the 2 to 8 sp3 carbon atoms present on the fullerene corexe2x80x9d. The more preferred is xe2x80x9ca hydrocarbon group which has 1 or 2 straight-chain or branched-chain substituent group(s) each comprising 2 to 8 nitrogen atoms and 2 to 20 carbon atoms, and is configured to be bonded to two of the 2 to 8 sp3 carbon atoms present on the fullerene corexe2x80x9d.
The amino group in said xe2x80x9cnitrogen-containing hydrophilic side chainxe2x80x9d may be primary, secondary or tertiary and may form a nitrogen-containing heterocyclic group [such as 3 to 8 (preferably 5 or 6)-membered unsaturated hetero-monocyclic groups containing 1 to 4 nitrogen atom(s) (e.g. pyrrolyl, pyrrolinyl, imidazolyl, pyrazolyl, pyridyl, dihydropyridyl, pyrimidyl, pyrazinyl, pyridazinyl, triazolyl, tetrazolyl, etc.); and unsaturated fused heterocyclic groups containing 1 to 4 nitrogen atom(s) (e.g. indolyl, isoindolyl, indolidinyl, benzimidazolyl, quinolyl, isoquinolyl, indazolyl, benzotriazolyl, acridinyl, etc.)]. Furthermore, it may optionally be substituted by lower alkyl or the like.
The xe2x80x9cnitrogen-containing hydrophilic side chainxe2x80x9d mentioned above may have other hetero atoms, such as oxygen, sulfur, etc., as its constituent atoms and/or substituents.
Furthermore, when two or more xe2x80x9cnitrogen-containing side chainsxe2x80x9d are present, there may be a cross-linking alkylene moiety bridging such nitrogen-containing hydrophilic side chains.
The xe2x80x9chydrocarbon groupxe2x80x9d of the xe2x80x9cnitrogen-containing hydrophilic side chainxe2x80x9d includes straight-chain, branched-chain, or cyclic hydrocarbon groups, whether saturated or unsaturated, and is preferably a hydrocarbon group of 1 to 20 carbon atom(s) (more preferably of 1 to 15 carbon atom(s)).
The specific structure of said xe2x80x9cnitrogen-containing hydrophilic side chainxe2x80x9d includes but is not limited to the following (the fullerene core is also shown). 
In the above formulas, Rs may be the same or different and each represents a straight-chain or branched-chain acyl group comprising 1 to 10 nitrogen atom(s) and 2 to 30 carbon atoms [more preferably [N-(N,N-di(lower)alkylamino)(lower)alkyl-N-(lower)alkyl]amino(lower)alkanoyl groups, [N-(N-(lower)alkylamino)(lower)alkyl-N-(lower)alkyl]amino(lower)alkanoyl groups, [N-pyrrolyl(lower)alkyl-N-(lower)alkyl]amino(lower)alkanoyl groups, [N-(N,N-di(lower)alkylamino)(higher)alkyl-N-(lower)alkyl]amino(lower)alkanoyl groups, [N-(N-(lower)alkylamino)(lower)alkyl-N-(lower)alkyl]amino(higher)alkanoyl groups, [N-pyrrolyl(higher)alkyl-N-(lower)alkyl]amino(higher)alkanoyl groups; groups of the formula: 
(wherein R1, R2, R3, R4 and R5 may each be the same or different over its occurrences and represents hydrogen or a lower alkyl group; A represents an alkylene group; Y represents CH or N, and n represents an integer of 1 to 4)]; straight-chain or branched-chain C2-30 alkyl groups comprising 1 to 10 nitrogen atom(s) and 2 to 30 carbon atoms [more preferably [N-(N,N-di(lower)alkylamino)(lower)alkyl-N-(lower)alkyl]amino(lower)alkyl groups, [N-(N-(lower)alkylamino)(lower)alkyl-N-(lower)alkyl]amino(lower)alkyl groups, [N-pyrrolyl(lower)alkyl-N-(lower)alkyl]amino(lower)alkyl groups, [N-(N,N-di(lower)alkylamino)(higher)alkyl-N-(lower)alkyl]amino(lower)alkyl groups, [N-(N-(lower)alkylamino)(lower)alkyl-N-(lower)alkyl]amino(higher)alkyl groups, [N-pyrrolyl(higher)alkyl-N-(lower)alkyl]amino(higher)alkyl groups; or groups of the formula: 
(wherein R1, R2, R3, R4, R5, A, Y and n are respectively as defined above; Axe2x80x2 represents an alkylene group)].
Ar represents an aryl group (e.g. phenyl, naphthyl, anthryl, etc.);
Rxe2x80x2 represents hydrogen or a lower alkyl group;
Ra and Rb may be the same or different and each represents hydrogen or a lower alkyl group, or Ra and Rb may, jointly and taken together with the carbon atom to which they are joined, represent a 3 to 6-membered cycloalkyl group.
A, A1, A2 and A3 may be the same or different and each represents an alkylene group;
X represents xe2x80x94Oxe2x80x94, xe2x80x94Nxe2x80x94 or xe2x80x94Sxe2x80x94; and
m represents an integer of 0 or 1.
It should, however, be understood that the various xe2x80x9cnitrogen-containing hydrophilic side chainsxe2x80x9d mentioned above are mere examples and, as the structure interposed between xe2x80x9cthe fullerene corexe2x80x9d and xe2x80x9cthe group of the formula 
the various known structures other than those illustrated above may also be selectively used.
The xe2x80x9clower alkyl groupxe2x80x9d or xe2x80x9clower alkyl moietyxe2x80x9d in the context of the present invention includes straight-chain or branched-chain groups each containing 1 to 6 carbon atom(s), such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, tert-pentyl, neopentyl, hexyl, isohexyl, etc.
The xe2x80x9calkylene groupxe2x80x9d includes straight-chain or branched-chain groups containing 1 to 10 carbon atom(s), such as methylene, ethylene, trimethylene, 2-methyltrimethylene, tetramethylene, ethylethylene, pentamethylene, 3-methylpentamethylene, hexamethylene, 2-ethyltetramethylene, heptamethylene, octamethylene, nonamethylene, decamethylene, etc.
The xe2x80x9chigher alkyl groupxe2x80x9d or xe2x80x9chigher alkyl moietyxe2x80x9d includes straight-chain or branched-chain groups each containing 7 to 20 carbon atoms, such as heptyl, octyl, 2-ethylhexyl, nonyl, decyl, 3,7-dimethyloctyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, 3-methyl-10-ethyldodecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, etc.
The number of xe2x80x9cnitrogen-containing hydrophilic side chainsxe2x80x9d on the fullerene core is preferably 1 to 4, and the presence of one or two such side chains is particularly preferred. When only one side chain is to be used, it is preferable to select a side chain containing a relatively large number of nitrogen atoms (preferably 4 or more N atoms). Particularly preferred is a polypyrrole which has a comparatively high binding affinity. When two side chains are to be involved, the use of alkylpolyamines containing 2 to 8 nitrogen atoms, which are comparatively less hydrophilic, is preferred.
Among the various fullerene derivatives described above, suitable derivatives can be judiciously selected in consideration of the ease of synthesis and the binding affinity for DNA, among other factors, but based on the information so far available, derivatives of the following general formula (I), inclusive of salts thereof, can be mentioned as preferred examples. 
[wherein the two Rs may be the same or different and each represents a straight-chain or branched-chain acyl group comprising 1 to 10 nitrogen atom(s) and 2 to 30 carbon atoms or hydrogen (provided, however, that the two Rs do not concurrently represent hydrogen)].
As the more preferred examples of the fullerene derivative, there can be mentioned derivatives of general formula (I) wherein the two Rs are the same or different and each represents a straight-chain or branched-chain acyl group comprising 2 to 8 nitrogen atoms and 2 to 30 carbon atoms as its constituent atoms.
As the still more preferred examples of the fullerene derivative, there can be mentioned derivatives of general formula (I) wherein the two Rs are the same or different and each represents a straight-chain or branched-chain acyl group comprising 2 to 8 nitrogen atoms and 2 to 20 carbon atoms as its constituent atoms.
Furthermore, fullerene derivatives of the following general formula (II): 
[wherein R represents a straight-chain or branched-chain acyl group comprising 1 to 10 nitrogen atom(s) and 2 to 30 carbon atoms and Rxe2x80x2 represents hydrogen or a lower alkyl group] inclusive of salts thereof can also be mentioned as preferred examples of the fullerene derivative.
As the more preferred examples of the fullerene derivative, there can be mentioned derivatives of general formula (II) wherein R represents a straight-chain or branched-chain acyl group comprising 2 to 8 nitrogen atoms and 2 to 30 carbon atoms.
The still more preferred examples of the fullerene derivative are derivatives of general formula (II) wherein R represents a straight-chain or branched-chain acyl group comprising 2 to 8 nitrogen atoms and 2 to 20 carbon atoms.
The above-mentioned fullerene derivatives and salts of the present invention can be synthesized by the processes known to those skilled in the art, either as such or as appropriately modified, according to the respective structures desired [cf. the literature cited above or below].
The method of producing the fullerene derivative of the invention is now described in further detail, taking fullerene derivatives having one or two nitrogen-containing hydrophilic side chainsxe2x80x9d as examples.
Process A (One Side Chain)
The organofullerene (methanofullerene, propanofullerene) obtainable by carrying out the known reaction of the vinylcarbene species thermally generated from a cyclopropenone acetal with fullerene (Literature 1; Tokuyama, H.; Isobe, H.; Nakamura, E., Bull. Chem. Soc. Jpn. 1995, vol. 68, 935-941) is subjected to a functional group transformation reaction to introduce a nitrogen-containing side chain. Methanofullerene and propanofullerene are respectively converted to hydroxy-containing organofullerenes, by the procedure which comprises adding water after the reaction of said vinylcarbene species to hydrolyze the ketene acetal in the case of methanofullerene and by the procedure which comprises hydrolytic removal of the acetal with the aid of the sulfuric acid catalyst in water/tetrahydrofuran/chlorobenzene and subsequent reduction with diisobutylaluminum hydride. The objective fullerene derivative can be synthesized by subjecting the thus-generated hydroxyl group to the following functional group transformation.
1. Known reaction (Literature 2, Nakamura, E.; Tokuyama, H.; Yamago, S.; Shiraki, T.; Sugiura, Y., Bull. Chem. Soc. Jpn. 1996, vol. 69, 2143-2151). By the coupling reaction of succinic anhydride and a hydroxy-containing organofullerene, the carboxylic acid derivative is prepared. This carboxylic acid and an amine compound having a primary or secondary amino function are subjected to coupling reaction to give the objective product.
As the amine compound mentioned just above, a polypyrrole derivative analogous to the netropsin derivative described in Literature 2, a polyamine such as an alkylspermidine or the like, and even acridine or the like which is intercalatable into the DNA base pair can be employed, for instance.
2. An xcex1-haloacid halide is coupled to a hydroxyl group-containing organofullerene (Literature 3: Boutorine, A. S.; Tokuyama, H.; Takasugi, M.; Isobe, H.; Nakamura, E.; Helene, C., Angew. Chem., Int. Ed. Engl., 1994, vol. 33, 2462-2465; Literature 4: An, Y. Z.; Chen, C. H. B.; Anderson, J. L. Sigman; D. S. Foote, C. S.; Rubin, Y., Tetrahedron, 1996, vol. 52, 5179-5189) to give an xcex1-halocarbonyl compound. The objective product can be obtained by coupling this halide to an amine compound having a primary or secondary amino function.
As this amine compound, the specific amine compounds mentioned hereinbefore can be employed.
These procedures can be applied to the known hydroxy-containing fullerene derivatives (Literature 4 cited above; Literature 5: Tokuyama, H.; Yamago, S., Nakamura, E.; Shiraki, T.; Sugiura, Y., J. Am. Chem. Soc., 1993, vol. 115, 7918-7919) in common.
Process B (2 Side Chains)
A fullerene derivative having more potent DNA-compacting activity can be synthesized from an organofullerene (bispropanofullerene) obtained by carrying out the known reaction of a biscyclopropenone acetal with a fullerene (Literature 6: Isobe, H.; Tokuyama, H.; Sawamura, M.; Nakamura, E., J. Org. Chem. 1997, vol. 62, 5034-5041) in conjunction with the procedure of said Process A by subjecting it to functional group transformation to thereby introduce hydrophilic residues. The functional group transformation of bispropanofullerene is carried out, just as mentioned above, by the hydrolytic removal of the acetal in the presence of the sulfuric acid catalyst in water/tetrahydrofuran/chlorobenzene and subsequent reduction with diisobutylaluminum hydride, whereby the bispropanofullerene is converted to an organofullerene having a couple of hydroxyl groups. In this procedure, a mixture of 8 different isomers inclusive of diastereomers is obtained, and the objective fullerene derivative can be synthesized by subjecting this mixture to the same functional group transformation as above.
1. Succinic anhydride is coupled to a hydroxy-containing organofullerene to give the carboxylic acid derivative. This carboxylic acid is coupled to an amine compound having a primary or secondary amino function to obtain the desired product.
As the amine compound, the same specific compounds as mentioned above can be employed.
2. An xcex1-haloacid halide is coupled to an organofullerene having two hydroxyl groups to give the corresponding xcex1-halocarbonyl compound. As the xcex1-haloacid halide for use in this procedure, xcex1-bromoacetyl bromide is known. As the halide, both the chloride and the bromide can be utilized and even the compound bearing a substituent in the xcex1-position can also be used. Regarding the organofullerene, a report is available on the derivatives having the C2 symmetry (Literature 7: Isobe, H.; Sawamura, M.; Nakamura, E., 13th Fullerene Symposium, 1997, 2-20, Nagano, Japan) but the equivalent or higher activity may be obtained by using organofullerenes of other symmetries as described in the above-cited Literature 6 or a mixture of isomers obtainable by said reduction with diisobutylaluminum hydride. The coupling of the resulting halide to an amine compound having a primary or secondary amino function, such as the compound mentioned above, gives the objective product.
The above amine compound includes the species mentioned hereinbefore.
The above procedures can be applied to any known fullerene derivatives having a plurality of hydroxyl groups (Literature 8: Taki, M.; Sugita, S.; Nakamura, Y.; Kasashima, E.; Yashima, E.; Okamoto, Y.; Nishimura, J., J. Am. Chem. Soc., 1997, vol. 119, 926) as well.
Those skilled in the art should be able to produce fullerene derivatives having desired structures in accordance with the invention by referring to the disclosures in the literature cited in this specification, known technologies, and the specific disclosures concerning Processes A and B, or working examples which are presented hereinafter.
The fullerene derivative of the present invention is an amphiphilic compound having excellent DNA-compacting activity. Permitting the fullerene derivative of the invention to act on DNA leads to the result that the derivative binds the DNA and the unimolecular DNA is bent and folded by the interbinding force acting between the intramolecular double strands. Furthermore, by the intermolecular binding force, a DNA condensate is produced. This compaction is reversible with respect to the concentration of the fullerene derivative and the regeneration of the DNA takes place upon extractive removal of the fullerene derivative.
The foregoing has been confirmed by the agarose electrophoretic analysis and AFM microscopic morphological observation of samples prepared by causing a varying concentration of the xe2x80x9ctetramine compoundxe2x80x9d, to be described below, to act upon the plasmid pBR322. This will be explained below using specific experimental data.
Test Compound
The fullerene derivative obtained in Example 1 which appears below (hereinafter referred to as xe2x80x9ctetramine compoundxe2x80x9d) was submitted to the experiment.
Electrophoresis Experiment Protocol
Electrophoresis was carried out in accordance with the method described in Short Protocols in Molecular Biology 3rd E., 1992, Wiley, 2-13.
As test samples, solutions prepared by dissolving the plasmid pBR322 (25 xcexcg/mL) and various amounts of xe2x80x9ctetramine compoundxe2x80x9d in 20% THF/HEPES-Mg buffer (20 xcexcL) were used. Each sample was incubated at 25xc2x0 C. for 5 minutes and then developed on an agarose gel using a buffer solution (5 xcexcL) containing 0.25% (w/v) Bromophenol Blue and 50% (v/v) glycerol. Electrophoresis was carried out using an ethidium bromide (0.5 mg/mL)-containing 1% (w/v) agarose gel/TBE buffer solution. The integrated optical density (IOD) of the fluorescent emission photograph was measured using NIH Image Program vl. 60. By this method, the migration amount of DNA was determined.
Results
The details are shown in FIG. 1.
Depending on the concentration of xe2x80x9ctetramine compoundxe2x80x9d, a phase transition phenomenon occurred. Thus, the amount of DNA migration in agarose electrophoresis declined rapidly when the ratio of the number of molecules of fullerene derivative to the number of base pairs of DNA was 1/1 and became nil at 1/2.6.
In the AFM microscopic observation of the same samples in a thin film of water, quite dissimilar AFM images were obtained before and after phase transition. Compaction of the DNA began before onset of phase transition and it was confirmed that the polymolecular compact obtained after phase transition was a hydrophobic mass.
The above experimental results suggest that in order that a wholesome DNA compact may be formed, the ratio of the number of molecules of the fullerene derivative to the number of base pairs of DNA preferably lies within the range of 4:1 to 1:2.
The above formation of a DNA condensate by the fullerene derivative is carried out by mixing the two reactants in a suitable buffer. However, this is not an exclusive choice but any other method in routine use in the art can be employed. Moreover, the DNA condensate formed can be isolated by the routine procedure, for example by subjecting the DNA solution after phase transition to ethanol precipitation. Furthermore, by extracting the fullerene derivative from the solution of DNA which has been compacted by addition of the derivative with an organic solvent such as chloroform, regeneration of the original DNA can be achieved.
As mentioned hereinbefore, the DNA-compacting activity of the fullerene derivative is closely associated with its high binding affinity for DNA. For reference, results of a relevant experiment with said xe2x80x9ctetramine compoundxe2x80x9d are shown below.
Experimental Method
DNA-compacting activity was evaluated in an ethidium bromide displacement assay. This competitive binding assay was carried out according to the protocol described in Journal of Medicinal Chemistry, 21, 658-668 (1978).
Results
The xe2x80x9ctetramine compoundxe2x80x9d at a concentration of 1.9 xcexcM substituted 50% of ethidium bromide.
This result can be used as a reference in the molecular designing of a fullerene derivative which is particularly useful for carrying the present invention into practice and a derivative having an equivalent or higher binding affinity for DNA as compared with the compound mentioned just above is especially desirable.
For exploring into the mechanism of DNA compaction by the fullerene derivative of the invention, the following two experiments were performed.
Experimental Method
Measurement of the CD Spectrum
A solution of calf thymus DNA (average MW=8.6 MDa, 13 kbp, 42% GC, highly polymerized, type 1, Sigma) or plasmid pBR322 DNA (MW=2.83 MDa, 4361 bp, New England Biolabs) in HEPES-Mg buffer (40 mM HEPES, 10 mM MgCl2; pH=7.6) at a base-pair concentration of 100 mM was prepared and put in a quartz glass cell, and using a JASCO J-720 spectrometer the CD spectrum was measured at 25xc2x0 C. Furthermore, the nucleic acid-compacting fullerene derivative was added to the above solution at concentrations 10 to 200 mM and the CD spectra were measured.
Results
No change at all occurred in the DNA conformational CD spectra, indicating that the DNA retained the B-form.
Experimental Method
Measurement of DNA Melting Temperature (Tm)
A solution of calf thymus DNA (average MW=8.6 MDa, 13 kbp, 42% GC, highly polymerized, type 1, Sigma) in HEPES-Mg buffer (40 mM HEPES, 10 mM MgCl2; pH=7.6) at a base-pair concentration of 100 mM was prepared and the nucleic acid-compacting fullerene was added at a concentration of 10 mM.
The above solution was put in a quartz glass cell and while the temperature was raised from 60xc2x0 C. at a rate of 1xc2x0 C./min, the absorbance at the wavelength of 258 nm where the hypochromism of a DNA double-strand is observed, was measured with a JASCO J-720 spectrometer.
Results
The melting temperature of the double-strand was increased by 2.7xc2x0 C. to 74.2xc2x0 C. as compared with the case in which the nucleic acid-compacting fullerene was not added (71.5xc2x0 C.), indicating stabilization of the double-stranded structure.
The above experimental results strongly suggested the mechanism that the DNA unimolecule is folded as the result of an interaction between the nucleic acid-compacting fullerene and the hydrophobic moiety of DNA (e.g. the major grooves of a DNA) and an interaction between the nitrogen-containing hydrophilic side chain and the phosphate group of the DNA, and that the hydrophobic moieties of a large number of folded DNA unimolecules coalesce to cause said compaction.
It is quite a novel finding that the fullerene derivative of the present invention not only has a binding affinity for DNA but even has an ability to compact a polymolecular DNA.
Therefore, xe2x80x9cthe mode of use for DNA compactionxe2x80x9d and the mode of use as a xe2x80x9cDNA compaction reagentxe2x80x9d of the present invention include all possible embodiments exploiting the DNA-compacting activity of the fullerene derivative of the invention described hereinbefore. Included, among such embodiments, are the use as a DNA compaction reagent; use for introduction of a vector into cells; use for introduction of a DNA (or a derivative thereof) fragment such as an antisense DNA (or a derivative thereof) or a decoy DNA (or a derivative thereof) into cells; use for control of gene expression through the binding to a promoter or enhancer region; use for modulating the cell cycle through suppression of the conversion of a double-stranded DNA to a single-stranded DNA; and use for control of the PCR efficiency through adjustment of the melting point involved in the transition from a single-stranded DNA to a double-stranded DNA or from a double-stranded DNA to a single-stranded DNA. Furthermore, application to gene therapies is also within the purview.
In using the fullerene derivative in any of the above modes of use, the fullerene derivative or salt of the invention can be used as it is or in the form of a composition to accomplish the intended object.